This invention relates to the field of digital phase detectors as for a phase locked loop and more particularly to an integratable current-mode output stage therefor.
In a phase locked loop, the frequency of a local oscillator signal is controlled in response to the output of a phase detector which compares the oscillator frequency with an input signal frequency. The phase detector output is filtered to provide a DC control signal to the local oscillator. An active filter may be used in those systems requiring a high DC gain characteristic. To aid frequency acquisition, it is known to provide a switchable bandwidth which is wide when the local oscillator is far from the desired frequency and narrow when the difference is very small. In systems for accomplishing this the switching itself typically causes perturbations in the circuit which affect the error sensing mechanism.